Osmium (Latin Osmium) is a chemical element with atomic number 76 in the Periodic Table of Chemical Elements of D. I. Mendeleev, denoted by the symbol Os. Under standard conditions, it is a shiny silver-white metal with a bluish sheen.
Osmium is the heaviest of all metals (its density is 22.6 g / cm3) and one of the hardest, but at the same time it is brittle, and it is easily obtained from it into powder. It is a transition metal and belongs to the platinum group.
Osmium was discovered in 1804 by the English chemist S. Tennant in black powder remaining after dissolving platinum in aqua regia. It is characterized by the formation of tetroxide OsO 4 with a pungent odor. Hence the name of the element, derived from the Greek "osme" - smell.
The osmium content in the earth's crust is approximately 5 • 10-6% by weight. It occurs naturally in its native form as a solid solution with iridium (minerals nevyanskite and sysertskite).
Outwardly, osmium differs little from other metals of the platinum group, but it is he who has the highest melting and boiling points among all metals of this group, it is he who is the heaviest. It can also be considered the least "noble" of the platinoids, since in a finely divided state with atmospheric oxygen it is already oxidized at room temperature.
PHYSICAL PROPERTIES OF OSMIUM
Osmium is the densest precious metal. It is slightly more dense than the platinum element, iridium. The most reliable density values for these metals can be calculated from the parameters of their crystal lattices: 22.562 ± 0.009 g / cm3 for iridium and 22.587 ± 0.009 g / cm3 for osmium. According to the latest information, the density of osmium is 22.61 g / cm3.
Due to its hardness, brittleness, low vapor pressure (the lowest among all platinum metals), as well as a very high melting point, osmium is difficult to machine.
CHEMICAL PROPERTIES OF OSMIUM
When heated, osmium powder reacts with oxygen, halogens, sulfur vapors, selenium, tellurium, phosphorus, nitric and sulfuric acids. Compact osmium does not interact with acids or alkalis, but forms water-soluble osmates with alkali melts. Reacts slowly with nitric acid and aqua regia, reacts with molten alkalis in the presence of oxidants (potassium nitrate or chlorate), molten sodium peroxide. In compounds, it exhibits oxidation states from -2 to +8, of which the most common are +2, +3, +4 and +8. Metallic osmium and all its compounds are easily oxidized electrochemically to OsO4.
Being in nature
In nature, osmium occurs mainly in the form of a compound with iridium, which is part of either native platinum or platinum-palladium ore. The minerals considered as raw materials for the extraction of osmium contain, on average, one thousandth of a percent of the heavy "relative" of platinum. During the entire period of exploration, not a single osmium nugget, even the smallest size, has been mined.
Osmium is used in many alloys, making them very wear resistant. If you add osmium to any alloy, then it immediately acquires incredible wear resistance, becomes durable, and increases its resistance to mechanical stress and corrosion.
Alloying of alloys is one of the main tasks, the solution of which is sometimes assigned to osmium. In combination with tungsten, nickel and cobalt, osmium becomes a "worker" in the electrochemical industry. Osmium alloy contacts, ferrules and ferrules are renowned for minimal wear.
The introduction of hard and heavy platinoid into the material sharply increases the wear resistance of rubbing pairs. Very little osmium is needed to give the metal-ceramic cutter special strength. Microscopic additions of osmium to steel of cutting grades make it possible to create the sharpest blades of technical, medical, and industrial knives.
Fountain pens with osmium nibs can write for years, which is not the case with all gold or other metallic nibs - osmium nibs are truly "no wear and tear."
An alloy of platinum (90%) and osmium (10%) is used in surgical implants, such as pacemakers, and in pulmonary valve replacement.
Alloy "osram" (osmium with tungsten) was used to make filaments of incandescent lamps.
Since osmium has no magnetic properties, it is actively used in the creation of watch movements and compasses.
Osmium catalysts are used in the hydrogenation of organic compounds, in the production of drugs, and in the synthesis of ammonia. Osmium tetroxide (a higher oxide, OsO4) finds its application as a catalyst in the production of some synthetic drugs, as well as in laboratory research - it is convenient to use it to stain tissues under a microscope.
Solid and non-magnetic osmium is used to make axles, supports and support sockets for high-precision measuring instruments. And although ruby supports are harder and cheaper than osmium, metal resistance is sometimes preferable for instrumentation.